364 Scientific Proceedings, Royal Dublin Society. 



de Phys. lxi. p. 161, 1861). Theodore du Moncel discovered that 

 the glowing part of the discharge, or aureole which surrounds the 

 fiery path, could be blown aside by a current of air driven into the 

 spark (Comptes rendus, xl. p. 313). Perrot, in a later publication, 

 " Sur la nature de l'etincelle d'induction de l'appareil Buhmkorff " 

 (Ann. de Chim. et de Phys. lxi. p. 200, 1861), deals with the 

 nature of the discharge, and proves by a series of ingenious and 

 interesting experiments, that the spark is composed of two parts, 

 of which the fiery track, or central portion, is a statical discharge ; 

 the aureole, or flame, is dynamical, and capable of electrolytic 

 action. The two were separated, and their actions studied apart. 

 Lissajous, by means of his well-known method of experimenting, 

 showed that the luminous flame, or aureole, continues to glow for 

 the fraction of a second, whereas the more brilliant fiery track 

 appeared to him to be instantaneous in its passage. This latter he 

 suggested is composed of incandescent particles, torn off the elec- 

 trodes, which form an incandescent and conducting arc. Perrot 

 confirmed this latter view, and stated that, with a condenser in 

 circuit, the path of the spark is intensely brilliant, but there is 

 little or no flame. 



An elaborate paper by Feddersen (Ann. de Chim. et de Phys. 

 lxix. p. 178, 1863) established the principles of the mechanism of 

 the Leyden jar discharge. By direct photographs he showed the 

 nature of the discharge, and with the aid of a rotating concave 

 mirror he proved that the apparently simple spark was exceed- 

 ingly complex, being composed of an initial discharge, followed 

 by as many as 100,000- or 1,000,000 sparks, oscillating between 

 the electrodes in a second of time. These oscillations were ren- 

 dered visible on a photographic plate, and his paper is illustrated 

 by drawings copied from photographs. Kirchoff showed that 

 Feddersen's result could be deduced mathematically; without 

 demonstration in fact (Poggendorff's Ann. exxi. pp. 551-566, 

 1864). Von Helmholtz, Sir William Thomson, and Eiess have 

 also dealt with this matter. Poggendorff, in his Anna ten (exxxii. 

 pp. 107-134), proved that in induction coils the negative is the 

 hotter pole. It is the reverse with currents, continuous discharges, 

 and with the brush discharge. The temperature varies with the 

 form, the nature, and the distance between the electrodes. Dewar 

 measured the temperature of the electric spark, and found it to 



